The present invention relates to the tracking of transitions within a bit stream, in particular for tracking of transitions within a bit stream of an output signal of an electronic device to be tested.
Integrated Circuits (IC) generally need to be tested to assure proper operation. This—in particular—is required during IC development and manufacturing. In the latter case, the ICs are usually tested before final application. During test, the IC, as device under test (DUT), is exposed to various types of stimulus signals, and its responses are measured, processed and usually compared to an expected response of a good device. Automated test equipments (ATE) usually perform these tasks according to a device-specific test program. Examples for ATE are the Agilent 83000 and 93000 families of Semiconductor Test Systems of Agilent Technologies. Details of those families are also disclosed e.g. in EP-A-859318, EP-A-864977, EP-A-886214, EP-A-882991, EP-A-1092983, U.S. Pat. Nos. 5,499,248, 5,453,995
The output signals of modern integrated electronic circuits often exhibit non-deterministic clock latencies between activities even if they are stimulated with the same stimuli. During production test of those devices, prior art test equipment does a timing test by strobing the bit stream with a fixed timing. In the presence of a timing drift, this test will fail, even though the DUT is operating correctly.
The reasons for non-deterministic output timing are beyond others process variations causing unknown but static timing variations, temperature variations of the clock insertion delays causing unknown and time varying timing drift.